Make every identity editable: agent and operator names plus avatars

- Migration 049: avatar_emoji/avatar_color on agents and employees
- updateAgent accepts a new name (mention-name validated) and avatar;
  new updateEmployeeProfile renames the operator and sets their avatar
- Avatars are emoji-on-color tiles (renderer CSP blocks remote images);
  an AvatarDirectoryContext built from the snapshot lets the shared
  Avatar component honor custom looks at every call site - chat rows,
  conversation list, org chart, office card, sidebar - without
  threading props through pages
- Team edit dialog gains Name + avatar editor (CEO included); the
  sidebar foot opens an Edit-profile dialog for the operator
- e2e: rename an agent to a new mention handle with an emoji avatar,
  edit the operator profile, both verified in the live shell

src/preload/index.ts

@@ -15,6 +15,7 @@ const api: DesktopApi = {
   deleteOrganization: (input) => invoke(IPC_CHANNELS.deleteOrganization, input),
   createAgent: (input) => invoke(IPC_CHANNELS.createAgent, input),
   updateAgent: (input) => invoke(IPC_CHANNELS.updateAgent, input),
+  updateEmployeeProfile: (input) => invoke(IPC_CHANNELS.updateEmployeeProfile, input),
   createTask: (input) => invoke(IPC_CHANNELS.createTask, input),
   updateTask: (input) => invoke(IPC_CHANNELS.updateTask, input),
   deleteTask: (input) => invoke(IPC_CHANNELS.deleteTask, input),